Generally, as a construction machine, a hydraulic excavator is constituted by an automotive lower structure, an upper revolving structure which is rotatably mounted on the automotive lower structure, and a working mechanism rotatably mounted on a front side section of the upper revolving structure.
Normally, the upper revolving structure on a hydraulic excavator of this sort is largely constituted by a revolving frame, an engine which is mounted on a rear side section of the revolving frame, a counterweight which is attached to rear end of the revolving frame at a position on the rear side of the engine, a floor panel which is provided on the revolving frame at a position on the front side of the engine, an operator's seat which is provided on the floor panel for an operator, and a housing or cover structure like a canopy or a cab which covers the upper side of the operator's seat.
Among hydraulic excavators, there are small-size hydraulic excavators, the so-called “mini shovels”, which are suited particularly for use on narrow working sites. In the case of small-size hydraulic excavators, it is difficult to secure a space for installation of a control valve, a swing motor or other equipments. Therefore, it is often the case to accommodate these equipments under a floor panel or between a floor panel and a revolving frame.
In such a case, it has been the usual practice to provide a tilt-up mechanism in association with a floor panel thereby to lift up one end of the floor panel away from the revolving frame. For example, at the time of maintenance and service, the floor panel is tilted up to allow easy access to control valve, swing motor or other equipments which are located under the floor panel.
More specifically, a floor panel support mechanism is provided between fore ends of a revolving frame and a floor panel to support the floor panel, permitting the floor panel to turn up and down in forward and rearward directions together with an operator's seat and a housing, about a supporting point which is provided at the front end of the floor panel. Further, it has been known to provide gas dampers of a tilting mechanism under the floor panel thereby to tilt up and down the floor panel in upward or forward direction, turning about a supporting point on the floor support mechanism (e.g., as disclosed in Japanese Patent Laid-Open No. 2000-72048).
In the case of hydraulic excavators in general, for the purpose of improving working environment of operator, a plural number of vibration insulating members are provided between a revolving frame and a floor panel to damp vibrations which would be transmitted from the revolving frame to the floor panel. These vibration insulating members are located, for example, in each one of front and rear side sections of a floor panel, connecting the floor panel to the revolving frame while resiliently supporting the floor panel from beneath (e.g., as disclosed in Japanese Patent Laid-Open No. H6-136787).
In the case of the above-mentioned hydraulic excavators of the prior art, attempts have been made to reduce discomfort and fatigue of an operator who is seated on the operator's seat, by providing a plural number of vibration insulating members between the revolving frame and the floor panel, for preventing transmission of vibrations from the revolving frame to the floor panel during a ground excavating operation or in a vehicular traveling operation.
However, in the case of a hydraulic excavator with such vibration insulating members, it is necessary to detach vibration insulating members in a rear side section from the revolving frame or from the floor panel to disconnect the floor panel from the revolving frame before lifting up the rear side of the floor panel and tilting up forward direction together with an operator's seat and a housing.
The vibration insulating members of this sort are constituted, for example, by large number of parts such as a resilient rubber bush, a sleeve which plays a role of positioning the rubber bush, a washer and a bolt for anchoring the respective parts. Therefore, at the time of dismantling vibration insulating members, it becomes necessary to disassemble the large number of parts. This means that it takes a great deal of time and labor just for dismantling the vibration insulating members, making a tilt-up operation of the floor panel troublesome and time consuming.
Besides, as described above, at the time of lifting a rear side of the floor panel to tilt up the whole floor panel in forward direction together with an operator's seat and a housing, the center of gravity is shifted by the tilt-up operation, giving rise to a problems as described below.
Namely, when the tilt-up angle of the floor panel is still small, loads of the floor panel, operator's seat and housing act in rearward direction, tending to push down the rear side of the floor panel. However, as the tilt-up angle of the floor panel increases, the center of gravity is shifted to a position forward of a supporting point on the floor panel support mechanism, and as a result, the loads of the floor panel, operator's seat and housing act to become a reversal force which tends to push up the rear side of the floor panel.
As a consequence, in the case of a tilting mechanism using gas dampers or the like, as the tilt-up angle of the floor panel increases, loads of the floor panel, operator's seat and housing inversely act as a pulling force, imposing a great load on gas dampers to such a degree as to cause premature damages to the gas dampers, deteriorating their durability and the service life.